1. Field of Invention
The present invention relates to a method for performing a selective etching process, and more particularly to a method of selectively etching a silicon layer relative to a silicon-germanium layer using a dry plasma etching process.
2. Description of Related Art
Typically, during fabrication of integrated circuits (ICs), semiconductor production equipment utilize a (dry) plasma etching process to remove or etch material along fine lines or within vias or contacts patterned on a semiconductor substrate. The success of the plasma etching process requires an etching chemistry that includes chemical reactants suitable for selectively etching one material while substantially not etching another material.
For example, on a semiconductor substrate, a pattern formed in a protective layer can be transferred to an underlying layer of a selected material utilizing a plasma etching process. The protective layer can comprise a light-sensitive layer, such as a photoresist layer, having a pattern formed using a lithographic process.
Once the pattern is formed, the semiconductor substrate is disposed within a plasma processing chamber, and an etching chemistry is formed that selectively etches the underlying layer while minimally etching the protective layer. This etch chemistry is produced by introducing an ionizable, dissociative gas mixture having parent molecules comprising molecular constituents capable of reacting with the underlying layer while minimally reacting with the protective layer. The production of the etch chemistry comprises introduction of the gas mixture and formation of plasma when a portion of the gas species present are ionized following a collision with an energetic electron. Moreover, the heated electrons serve to dissociate some species of the gas mixture and create a reactive mixture of chemical constituents (of the parent molecules).
Thereafter, the ionized gas species and reactive mixture of chemical constituents facilitate the etching of various features (e.g., trenches, vias, contacts, etc.) in the exposed regions of the semiconductor substrate. Such substrate materials where etching is required include silicon oxide (SiOx), silicon nitride (SiNy), poly-crystalline silicon (polysilicon), and mono-crystalline silicon (silicon), and doped and un-doped silicon, for example.
In some etch applications, it is necessary to etch silicon-germanium with selectivity to silicon and, in other etch applications, it is necessary to etch silicon with selectivity to silicon-germanium. While dry plasma etching processes have been successfully developed to achieve etch selectivity in the former situation, dry plasma etching processes have been unsuccessful in the latter situation. As a result, users have turned to wet etching techniques to selectively etch silicon relative to silicon-germanium.